Electrical circuits for the production of musical tones



Dec. 8, 1925- 1,564,209

|. B. CRANDALL ELECTRICAL CIRCUITS FOR THE PRODUCTION OF MUSICAL TONESFiled June 9, 1921 P Sheets-Sheet 1 &

Dec. 8, 1925- 1,564,209

I. B. CRANDALL ELECTRICAL CIRCUITS FOR THE PRODUCTION OF MUSICAL TONES//"v/hy 5. Cranda/A Mai; A?

Patented Dec. 8, 1925.

STATES PATENT orrrce.

IRVING B. CRANDALL, OF WYOMING, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRICCOMPANY, INCORPORATED, OF NEW YORK, N. Y.,

A CORPORATION OF NEW YORK.

ELECTRICAL CIRCUITS FOR THE PRODUCTION OF MUSICAL TONES.

Application filed June 9,

To all whom it may] concern:

Be it known that I, IRVING 1%. CHANDALL, a citizen of the United States,residing at lVyoming, in the county of Essex and State of New Jersey,have invented certain new and useful Improvements in Electrical Circuitsfor the Production of Musical Tones, of which the following is a full,clear, conelse, and exact description.

This invention relates to electrical circuits for producing alternatingcurrents of different frequencies, and also to arrangements forconverting such currents into tones of varying pitch.

The invention has for an object the product-ion of tones which varywidely in pitch and at the same time are controlled as to volume.

A further object is to produce electric oscillations of variablefrequency and to control their amplitude at different frequencies.

In accordance with the invention a source of electric oscillations isprovided with means for changing the frequency, for example by changinga capacity or a c011- denser in a tuned circuit, and simultaneously withthe operation of the frequency changing means, a resistance in shuntacross the output circuit, or in series therewith, or both, is varied tocontrol the amplitude of the oscillation currents. This circuit isparticularly useful, when connected to a telephone receiver or otherdevice for converting electrical energy into sound energy, for thepurpose of testing the sensitivity of the ear to tones of differentpitch.

Oscillation generators frequently have the characteristic of producingcurrents of a greater amplitude at one frequency than at another. Forexample, the output energy may increase as the frequency is increased.In order to compare the sensitivity of the ear to a tone of one pitchwith that of another pitch, it is desirable to be able to control easilythe sound energy of the various tones used in testing. If a receivingdevice is used which acts to uniformly convert electrical energy intosound energy at all frequencies, it'is then necessary only to providemeans for giving a constant supply of electrical eaiergy, with means forchanging the energy by a known amount from a predetern'iined amountwhich may be taken as a standard. It is very difficult,

1921. Serial No. 476,169.

however, to design a receiver which will not be more responsive to somefrequencies than to others. This invention provides means adapted notonly to correct for changes in electrical energy output, but also tocorrect. for non-uniform translation through the receiver.

The above and other objects of the invention will be more fullyunderstood from the following detailed description taken in connectionwith the accompanying drawings, in which Fig. 1 shows the invention in acircuit employing a mercury arc oscillator, and Fig. 2 shows a modifiedform employing a vacuum tube oscillator.

Referring to the drawings by reference characters, the evacuated mercuryare device 10 and its associated circuit provide an oscillationgenerator operating on the principles outlined in Vreeland Patent No.973,826, dated October 25, 1910. The tube 10 contains a cathode 11 andoppositely positioned anodes 12. A battery or other source 13 suppliesdirect current through an inductance .15 and resistances 16 between thecathode and anodes. Vindings 18 and 19 serve the purpose of shifting theionization current between the cathode and anodes to produceoscillations, and also serve as primary windings for the secondarywinding 20, which is connected to the work circuit.

The windings 18 and 19 in conjunction with a series condenser such asthat shown at 22 also serve to control the frequency of theoscillations. A plurality of con densers like those shown in the drawingat 22,, 22 22 and 22, are employed for changing the frequency, one ofthese condensers being selectively thrown into the circuit by closingthe contacts 26,, 26 26 26 etc., of a plurality of keys A, B, M, N,etc., which, if desired, may be arranged as the keys of a musicalinstrument. The letters A, B, etc., represent the keys used for thelower frequencies, and the letters M, N, etc., represent the keys forthe higher frequencies. For the lower frequencies it is desirable tohave the windings 18 and 19 connected in series, as shown in thedrawing, and for the higher frequencies to have them connected'inparallel, a relay 2% being employed to change the windings from seriesto parallel relationship.

naeaaoe In order to purify the tones of harmonics or other undesiredfrequencies, a parallel resonant circuit for each frequency is connectedacross the secondary portion of the output circuit. For the frequencyrepresented by the key A this resonant circuit comprises" the condenser28 and the inductance 30 The inductance 30,, may be used for all of thelower frequencies represented by the keys A, B, etc., a separatecondenser such as 28,, 28 etc., being used with each of the keys of thisseries. For hi her frequencies an inductance 30 is substituted for 30,,and this is employed in conjunction with condensers 28 28 etc., for theseries of frequencies beginning with the key M. These keys are providedwith additional contacts 3%,, 32 etc., which close a circuit throughrelay 24: and relay 33 for changing windings 18 and 19 to the parallelarrangement and for changing from inductance 30 to 30 Each key isprovided also with a contact for connecting adjustable resistances 35,,35 35 35 etc., across the secondary circuit. The method of adjustingthese resistances will be described later.

The secondary circuit is also connected to a receiver R, which may bespecially designed to uniformly convert electrical oscillations intosound waves, or may have a non-uniform translating characteristic. Inthe latter case, if desired, a correcting circuit may be employedcomprising a parallel resonant circuit in series with the receiver,

having a condenser in one branch and an inductance 42 and resistance 44in the other branch, and a series resonant circuit across the linehaving a condenser 46, inductance 48 and resistance 50 in series. Thesecircuits are tuned to the frequency at which the receiver is 'mostsensitive, and tend to cut down the current at this frequency and tosome extent at adjacent frequencies. This arrangement is disclosed inthe copending application of E. C. Vente. Serial No. 482,729, filed July6, 1921, and need not further be described here. A current measuringinstrument 52' may be placed in the circuit connecting the oscillator tothe receiver R.

The operation of this circuit when used in ear analysis is as follows:

First, assuming that the receiver R or the receiver and its correctingnetwork, if the latter is employed, have a uniform translatingcharacteristic, the resistances 35 35 35 35 etc., may be initiallyadjusted so that at each frequency the same current is shown in themeter 52. This condition may be taken as a standard, and for comparisonof the sensitiveness of the ear at different frequencies, a tone of onefrequency,,produced by the standard amount of current as abovedescribed, is listened to. Another key may then be quickly depressed,and if the apparent loudness of this tone is different from that of thefirst tone, the corresponding resistance may be adjusted manually untilthe apparent loudness is the same. The relative difference in toneintensity may be determined from the readings of the meter 52 at the twoadjustments, or the resistances 35 may be calibrated in any desiredunits for giving a direct indication. It will be seen, therefore, that acurve can readily be made showing the amount of sound energy necessaryat a plurality of frequencies to give the same apparent loudness.

If a receiver is employed which has a nonuniform translatingcharacteristic and no correcting network is used, the amount of currentnecessary to give uniform sound intensity at various frequencies with agiven receiver can be determined by known laboratory methods, and theresistances 35 may beinitially adjusted so that the required current maybe immediately supplied when the respective keys are depressed. In thiscase it is desirable to calibrate the resistances with relation to somevalue of output sound energy arbitrarily taken as a standard. In thisway the resistances 35 take care of irregularities both in the source ofoscillations and in the receiver.

Referring now to Fig. 2, a three-electrode vacuum tube oscillator isemployed comprising the oscillator tube 55 and the amplifier tube 56,which is connected between the oscillator and the transformer 57.Oscillations are produced by reason of an inductive feed-back comprisingone or more of the windings 58, 59 and 60 in the input circuit of tube55 and the windings 58, 59 and (50 in the output circuit. Forcontrolling the frequency condensers 65 65 etc., may be selectivelyconnected across the winding 58, or a plurality of the windings 58, 59and 60,-as the case may be. As shown in the drawing, the lowerfrequencies, represented by keys A, B, etc., use only the windings 58and 58. Another series of keys beginning with M use the windings 58 and59 in series and windings 58' and 59' in series. Still another series ofkeys not shown may use all three windings in series. Tuned circuitscomprising condensers 28 28 28 etc., and inductances 30 ,'30 30, etc.,are employed for filtering, substantially as in Fig. 1. For controllingthe amplitude of the current, series resistances 7 5,. 75,;,, etc., andparallel resistances 76... 76 ,-76m. etc., may be employed. instead ofthe single resistances shown in Fig. 1. By using both series and shuntresistances the impedance of the secondary circuit to the amplifier 56may be maintained constant. The operation of the circuit of Fig. 2 issubstantially the same as that of Fig. 1.

While two embodiments of the invention of said oscillations, and meansmechamcal ly connected with said first means including an adjustableresistance for operation simultaneously therewith for controlling theamplitude of said oscillations.

2. In combination, a

, ond means being unequally efiicient at differa source of electricwaves ent frequencies, and means operably connectedwith said frequencychanging means for varying the current to correct said inequality.

4. In combination, a source of electric oscillations, manually operablemeans for changing the frequency of said oscillations, and preadjustablemeans including an adjustable resistance for determining the amplitudeat each of a plurality of frequencies.

5. In combination, a telephone receiver, for energizing said receiver,means for regulating the frequency of said waves, and means mechanicallyconnected to said first means for operation I simultaneously therewithfor regulating the mentioned means.

, keys for varying a tuned circuit for frequency, and means including,an adjustamplitude of said waves.

1 6. In'combination, a telephone receiver, a source of electric wavesfor energizing said receiver, means for regulating the frequency, meansmechanically connected to said first means for operation simultaneouslytherewith for controlling the amplitude of said waves, and means forcontrolling the amplitude of said waves independently of second 7. Incombination, an oscillation genera-.

' I tor having a tuned circuit, a plurality of reactance element insaidchanging the oscillation source of electric os source of electricoscillations, means connected to said source for able resistancecontrolled by said keys for varying the amplitude of said oscillations.

8. In combination, an oscillation generator havinga tuned circuit, aplurality of keys for varying a reactance element in said tuned circuitfor changing the oscillation frequency, mean including resistancecontrolled by said keys for varying the amplitude of said oscillations,and means operable independently of said keys for varying the amplitudeof said oscillations.

9. In combination, an oscillation generator. means forvarying thefrequency of said oscillations, a resistance in the output circuit ofsaid generator, and means mechanically connected with said first meansfor operation simultaneously therewith for varying 'said resistance.

'10. In combination, an oscillation generatorhaving a tuned circuit, aplurality of condensers adapted to be selectively connected in saidtuned circuit, and means for controlling the amplitude of saidoscillations simultaneously with the selection of said condensersrespectively.

11, In combination, tor, means for varying the frequency of sa1oscillations, a plurality of circuits selective to individualfrequencies, and means for simultaneously connecting any one of saidselective circuits to said generator and adjusting said generator toproduce a corresponding frequency. v

12. In an apparatus for testing the sen-sitiveness of the ear tosounds-means to produce sustained tones each of said tones having adifferent frequencv but the same intensity, means to vary the intensityof said tones to produce the same apparent loudness to the ear for allfrequencies, and means to measure the variations in intensity for eachfrequency. 7

13. In an apparatus for testing sensitiveness to sound, means forproducing tones of different frequencies, and means for preadjustingsaid tone producing means to -obtain the same constant intensity at allfrequencies.

an oscillation generafor producing tones of for preadjusting toeqnalconstant nessto sound, means various frequenc es, means said toneproducing" means ass intensity at all frequencies. and means for varyingthe intensity of said tones.

Inwitness whereof, I hereunto subscribe my name this 7th day of June, A.D. 1921.

IRVING B. CRANDALL.

